This application claims the priority of German patent document 199 32 781.5, filed Jul. 14, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process and apparatus for supplying electric energy to the wiring of a motor vehicle.
German Patent Document DE 197 03 171 A1 discloses a vehicle with a driving internal-combustion engine and an energy source assigned to the latter, as well as electric consuming devices. The consuming devices are supplied with electric energy by a current generating device in the form of a fuel cell unit which can be activated independently of the operation of the internal-combustion engine. Parallel to the consuming devices, which can be energized by the fuel cell unit, a buffer battery is provided for covering short-term demand peaks, such as occur, for example, when starting the internal-combustion engine.
In German Patent Document DE 195 23 109, a motor vehicle driven by an internal-combustion has a fuel cell system for generating electric energy for operating electric consuming devices, instead of a generator. The electric energy for starting the fuel cell system (or a splitting system assigned to the latter) is provided by a battery. In this case, it can be provided that a voltage regulator adapts the output voltage supplied by the fuel cells for supplying consuming devices with electric energy according to the requirements. The provision of such a voltage regulator between the fuel cell system and the vehicle wiring was found to require relatively high expenditures.
It is an object of the invention to provide a process and apparatus for electrically energizing a vehicle wiring system, using a fuel cell system for generating current, in a particularly simple manner.
This and other objects and advantages are achieved by the circuit arrangement according to the invention, in which an electronic power system for adapting the voltage between the fuel cell system and the vehicle wiring is unnecessary. Because of an electric interaction between the individual current generating components for the vehicle wiring, higher efficiency of the overall system is obtained. In addition, the overall system can be provided at a lower cost in comparison to conventional solutions.
According to the invention, a low-cost, optimal adaptation of the fuel cell system is provided to a changeable current demand of the vehicle wiring. The battery can be charged by the fuel cell, simultaneously with or independently of a supply of the vehicle wiring with energy. The process according to the invention, makes it possible to operate the fuel cell unit constantly at nominal capacity because a generated current can optionally be supplied to the battery and/or a consuming device.
The fuel cell unit is activated when the battery voltage falls below a preadjustable limit for charging the battery and optionally for at least partially supplying the vehicle wiring with electric energy. This measure ensures optimal utilization of the energy provided by the respective current supply components. This measure can e used with particular advantage when the vehicle engine is switched off.
In addition, the fuel cell unit can be activated when the vehicle wiring load exceeds a preadjustable limit. As a result, it is possible, for example, to design a battery, and even an existing generator, to be relatively small in comparison to conventional arrangements because, when a defined vehicle wiring load is exceeded, the fuel cell unit can take over the load to a maximum possible power output. Furthermore, the fuel cell unit is deactivated when a preadjustable battery voltage limit is exceeded. As a result, the battery can be protected from damage due to overcharging.
According to a particularly preferred embodiment, the circuit arrangement according to the invention has a diode which is connected between the battery and the fuel cell unit. As a result, current flow in only on direction between the fuel cell unit and the battery or the vehicle wiring is ensured in a simple manner.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.